This invention relates generally to the punch and die arts and more particularly to a stripper device for stripping a workpiece from a punch upon extraction of the punch from the workpiece.
Punch and die operations are a common, widely used and well known operation in the metal processing industry. Punch and die sets are typically used for forming holes through workpieces and provide a high degree of accuracy, speed and efficiency in forming such holes. In a typical punch and die operation, a punch is attached to a punch press and is alignably positioned over a complementary stationary die into which it projects when compressed by the punch press. A workpiece is positioned between the punch and the die and the punch press is operated to force the punch through the workpiece and into the die thereby forceably removing a slug from the workpiece and creating a hole in the shape of the punch cross-section.
Since the punching operation is accomplished by applying substantial forces to the punch in order to force it through the workpiece, the workpiece tends to bind against the punch when the punch is extracted from the newly formed hole. The prior art resolved binding problems by utilizing a stripper which held the workpiece firmly against the die. Heretofore, typical strippers have been relatively large, generally U-shaped metal brackets or bars which are held forceably against the workpiece and having a large opening through which the punch traverses freely when advancing and retracting relative to the workpiece. The physical contact between these strippers and a workpiece permit the stripper to retain the workpiece against the die. When the punch is retracted, the stripper continues to push against the workpiece providing counteracting forces to overcome the binding forces of the workpiece on the punch.
While prior art strippers help eliminate problems caused by the workpiece binding on the punch, they are typically large unwieldy pieces and difficult to use along edges or in channel areas due to their general configuration and relatively large size. To overcome this problem, specific strippers were designed for specific problem situations. Accommodating specific problems with specifically designed strippers resulted in a wide variety of strippers requiring additional maintenance, inventory and cost.
An additional problem caused by all prior art strippers is that undesirable markings or even indentations are created on the abutting surface of the workpiece due to the forceful downward impact against the workpiece when the punch is upwardly extracted. The resulting marks and/or indentations sometimes must be worked out of the surface of the workpiece thereby increasing the time, worker effort and cost of the punching operation.
In order to overcome the problems of rigid strippers, it has heretofore been proposed to use a relatively hard neoprene sleeve on the theory that the spring-like action of the sleeve will have a stripping action similar to the stripper bar in the punching operation. A neoprene sleeve of this type is formed generally of a cylindrical shape being somewhat longer than the operative length of the punch. The additional length of the stripper sleeve positions the punch a distance away from the workpiece prior to punching. The stripper sleeve provides an elastically biasing body which acts to strip the work from the punch upon retraction of the punch.
While the stripper sleeve helps to prevent marking of the abutting workpiece surface, problems have arisen in that the stripper has commonly been attached directly to the punch thereby requiring a new punch and stripper combination each time the punch size is changed or the punch needs to be replaced. It would be preferred to replace the stripper sleeve only when required, as when a punch of a substantially different size or cross section is desired and not at every instance in which a punch is changed or replaced.